COEUR D'ALENE, Idaho  The region's largest infestation of mountain pine beetles in 20 years has hit more than a million acres of forests in northern Idaho and Montana, while 2.5 million acres in Washington face disease and insect problems.

Recent flight surveys by the U.S. Forest Service and state forest management agencies found that years of drought have left forests in the Northwest vulnerable.

The surveys found that 1.1 million acres of forest came under attack by mountain pine beetle in northern Idaho and Montana in 2005, an increase from the 675,000 acres the year before.

The Washington Department of Natural Resources reported that mountain pine beetles were at "epidemic" levels, with a 28 percent increase to 554,000 acres. Overall, insect and disease problems are present in 2.5 million of Washington's 21 million acres of forest, up from 1.9 million acres the previous year.

Karen Ripley, an entomologist with the Washington Department of Natural Resources, said last year's abundant rain and this winter's good snowpack will reduce the stress on the region's forests.

But she said it would take several years of normal moisture for forests to return to health. She said fire suppression combined with a lack of logging means nature will find a way to remove trees.

"Nature's way is to have some of the beetles kill some of the trees," Ripley told The Spokesman-Review. "That relieves some of the competition. We've got a lot of stressed trees out there now, and they're easy pickings."

In the Bitterroot Mountains along the Montana-Idaho border, the beetles have left orange patches of dead trees, said Tom Martin, a silviculturist with the Idaho Panhandle National Forest.

He said the Forest Service wants to thin about 500 acres in the Upper St. Joe River area of Idaho to reduce the infestation. The agency, he said, has also spent $40,000 to protect lodgepole pine at the Lookout Pass Ski Area with pheromone treatments. The treatments fool beetles into thinking a tree has already been attacked.

"What we're trying to do is weather the storm," said Martin.

The survey found that populations of other bark beetles in the Idaho Panhandle National Forest were "much reduced."

"Things can change rapidly, but the last couple of years we've gotten favorable moisture," Martin said.

In the Colville National Forest in eastern Washington, fir engraver beetles appear to be increasing, infesting about 368,000 acres of forest in 2005. That's up 20 percent from the previous year.

Douglas fir beetles have infested about 69,000 acres in eastern Washington, up from the 50,000 acres where they were found the previous year.

Mountain pine beetles have also been a problem in British Columbia, where at least 20 million acres of forest have been killed.

Officials there say warmer-than-average winters have led to the outbreak.